Device for hydraulically adjusting the rollers of strand guiding segments of a continuous casting installation

ABSTRACT

A device for hydraulic adjustment of rollers of strand guiding segments of a strand casting device has hydraulic cylinders which are separated by a piston with piston rod into a cylinder chamber and an annular cylinder chamber, respectively. The cylinder chambers can be connected by control members alternatingly and in opposite directions as well as simultaneously with a pressure source and a pressure sink, wherein on-off valves are provided as control members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for hydraulically adjustingcomponents, in particular, rollers of strand guiding segments of acontinuous casting installation, comprising hydraulic cylinders whichare separated by a piston with piston rod into a cylinder chamber and anannular cylinder chamber, respectively, wherein the cylinder chamberscan be connected by control members alternatingly and in oppositedirections as well as simultaneously with a pressure source and apressure sink.

2. Description of the Related Art

In continuous casting installations the casting process begins in acasting mold. The surficially solidified casting strand exits from themold vertically and is deflected by 90° in strand guiding segmentshaving a certain radius and is guided to a horizontal straighteningdriver arranged downstream. The guiding of the casting strand isrealized by guiding rollers which can be adjusted by hydrauliccylinders. Accordingly, it is possible to consider, inter alia, rollwear and changed casting parameters. For controlling the hydrauliccylinder, in general, proportional servo valves are used. They requiremicrofine-filtered hydraulic oil as a result of their precise fit. Theexpenditure in regard to oil filtering is significant. Moreover, thereis always a fire danger in connection with hydraulic oil in a castingmachine and rolling mill area.

SUMMARY OF THE INVENTION

The invention has the object to provide a hydraulic system for adjustingcontinuous strand guiding segments which has a comparatively minimalrequirement with regard to the purity of the working liquid and theminimal fire danger.

The object is solved in that as control members on-off valves areprovided. On-off valves are either closed or open while proportionalservo valves can also be in any intermediate position. Accordingly,on-off valves can withstand coarse dirt particles without clogging,while the possible opening of a proportional servo valve requires aclean working medium in order to prevent seat soiling. Moreover, incontrast to the proportional servo valves, the valve pistons of theon-off valves do not require precise fit because in the open state theyare centered on a stop and in the closed state on the seat. Accordingly,the requirement with regard to purity and, moreover, to the lubricationaction of the working fluid in the case of on-off valves issignificantly lower than in the case of proportional servo valves. Thismeans a reduced expenditure for filtering and the problem-free use ofwater-oil emulsions as a working liquid. In addition to the reducedexpenditure for the on-off valves and for the type as well as thecleaning of the working liquid, the fire safety is a decisive advantageof the solution according to the invention.

By arrangement of four on-off valves in a full bridge circuit, a simpleguiding and minimal length of the hydraulic lines with correspondingminimal installation expenditure are achieved.

It is also advantageous that the on-off valves are controllable by athree-step controller. The three-step controller operates only with thepositions plus, minus, and zero. In the plus position, one of the on-offvalve pairs is excited, in the minus position the other one, while inthe zero position both on-off valve pairs are without current and thusclosed. This results in a simple control configuration.

Since the on-off valves have a throttle, an adjustment of the pistonposition without overswinging can be realized despite the fully openon-off valves.

It is also advantageous when the on-off valves can be controlled bypulse width modulation. While in the three-step control the opening timeinterval of the on-off valves as a whole can be varied, the number ofconstant, short opening intervals is variable in connection with thepulse width modulation (variable pulse-duty factor). This is realized,similar to the three-step control, by means of discrete switchingsignals of a separate electronic hardware or by means of software of acomputer. This optimizes the pulse-duty factor in the direction ofswitching frequency reduction. In the pulse width modulation, as in thecase of the three-step control, an outlet on-off valve and an inleton-off valve are always controlled at the same time since the inflowvolume of one cylinder chamber corresponds always to the outflow volumeof the other one.

It is moreover advantageous that each piston is connected by means of aconnecting rod with a position transducer which triggers the controlwhen the piston position surpasses an upper or a lower limit value. Theposition transducer allows a closed control circuit for the pistonposition. In this connection, a simple configuration and a simplestartup of the three-step controller results based on the determinationof hysteresis of the permissible piston position by an upper and lowerlimit value thereof.

Since the four on-off valves are combined to an on-off valve block, aspace-saving, cost-efficient configuration of the on-off valves isprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention result from result from the claims,the subsequent figure description and the drawings, in which embodimentsof the invention are schematically illustrated.

It is shown in:

FIG. 1 a circuit diagram of the bridge circuit of the hydraulic oilcirculation of a hydraulic cylinder;

FIG. 2 a circuit diagram of the hydraulic oil circulation and thecontrol of the on-off valves of a hydraulic cylinder;

FIG. 3 a simplified circuit diagram of the hydraulic oil circulation andthe control of the on-off valves of the four hydraulic cylinders of astrand guiding segment;

FIG. 4 like FIG. 3, but with perspective illustration of a strandguiding element.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the on-off valves (1 a, b, c, d), connected in a bridgecircuit, of the hydraulic circuit of a hydraulic cylinder (2) which arecombined to a valve block (3). The on-off valves (1 a, b) can beconnected via a first connecting point (4) with a pressure sink (5), theon-off valves (1 c, d) via a second connecting point (6) with a pressuresource (7). The on-off valves (1 a, c) are connected moreover via athird connecting point (8) with a cylinder chamber (9), the on-offvalves (1 b, d) via a fourth connecting point (10) to an annularcylinder chamber (11) of the hydraulic cylinder (2). The cylinderchamber (9) and the annular cylinder chamber (11) are seal-tightlyseparated by a piston (12). The piston has a piston rod (13) projectingfrom the annular cylinder chamber (11). FIG. 1 shows the very compactconfiguration of the valve block (3) which is realized with minimalexpenditure.

In FIG. 2, a valve block with a hydraulic cylinder (2) and a simplifiedillustration of the electric control of the on-off valves (1 a, b, c, d)are illustrated. FIG. 2 shows also the connecting points (4, 6, 8, 10)for connecting the on-off valves (1 a, b, c, d) with the pressure sink(5) and the pressure source (7), the cylinder chamber (9) as well as theannular cylinder chamber (11). The piston (12) is connected by aconnecting rod (14) with a position transducer (15) which indicates therespective position of the piston (12) relative to the hydrauliccylinder (2). Each one of the on-off valves (1 a, b, c, d) has asolenoid (16) which is connected via electric lines (17 a, b, c, d) witha three-step controller (18) or a pulse width modulator (19). Thethree-step controller (18) and pulse width modulator (19) are realizedas electronic hardware or integrated as software in a computer (20). Theon-off valves (1 a, b, c, d) have springs (21) which effect theirclosing when the solenoid (16) is without current. The piston rods (13)are sealed by glands (22) which also serve for supporting the hydrauliccylinders (2) on one half of the strand guiding segments (35, FIG. 4).They support on their free ends a swivel head (23) for connecting themwith the other half of the strand guiding segments (35).

FIG. 3 shows a simplified circuit diagram of the hydraulic oilcirculation and the control of the valve blocks (3) for the fourhydraulic cylinders (2) of a strand guiding segment (35, FIG. 4). In thesame way, it is also possible to adjust leveling machines and saws. Aswitch cabinet (24) is connected with a computer whose software controlsthe on-off valve blocks (3) by means of three-step controllers or pulsewidth modulation. The switch cabinet (24) has inter alia a network card(26), a central processing unit (CPU) (27), a memory (28), an interface(29), for example, a SSI interface for establishing a connection to theposition transducer (15), a digital/analog converter or switchingamplifier (30) for the on-off valve signals, a digital input/output (31)for a control panel (32) on site and for a strip terminal (33) forconnecting the signals of the device; in addition, a mains supplycircuit (34) is provided.

FIG. 4 shows basically the same as FIG. 3 but with a strand guidingsegment (35) in a perspective illustration. The latter has rollers (36)between which the cast strand (37) to be guided is positioned. Therollers have supports (38). The latter are adjusted by the hydrauliccylinders (2) and the pistons (12) by means of the piston rod (13).Pressure transducers (39) for monitoring the process are mounted in thehydraulic lines between the on-off valve blocks (3) and the hydrauliccylinders (2). Their signals are collected together with the signals ofthe on-off valve block (3) in an input/output component (40) andtransmitted to the digital/analog converter (30). The signals of theposition transducer (15) are then transmitted to the interface (29).

The device according to the invention functions as follows. When theposition transducer (15) shows a deviation from the nominal position ofthe rollers (36), the nominal position is adjusted again, once a certainupper or lower limit value is surpassed, by controlling thecorresponding on-off valves (1 a, b, c, d) via three-step control orpulse width modulation.

By employing the on-off valves instead of proportional servo valves awater/oil emulsion can be used as the working liquid so that the firedanger in the case of leakage is reduced. Moreover, a microfinefiltration of the working liquid is no longer needed so that the deviceaccording to the invention is less expensive with regard to initialinstallation cost and operation.

What is claimed is:
 1. A strand guiding segment (35) of a strand casting device with rollers (36) between which a cast strand (37) is guided, wherein the rollers (36) are configured to be moved toward one another by supports (38), the strand guiding segment (35) comprising: at least four hydraulic cylinders (2) with pistons (12) and piston rods (13) configured to move the supports (38); four on-off valves (1 a, b, c, d), connected in a full bridge circuit and combined in a valve block (3), provided for each one of the hydraulic cylinders (2) for advancing the hydraulic cylinders (2); a computer (25) having a software for controlling the on-off valves by pulse width modulation or three-step control; pressure sensors (39) arranged in hydraulic lines between the valve blocks (3) and the hydraulic cylinders (2); position transducers (15) connected to the pistons (12); a switch cabinet (24) connected to the computer and configured to receive signals, generated by the pressure sensors (39), the position transducers (15) and the valve blocks (3), and to send the signals received to the computer (25).
 2. The strand guiding segment according to claim 1, wherein the on-off valves (1 a, b, c, d) have a throttle.
 3. The strand guiding segment according to claim 1, wherein each piston (12) is connected by a connecting rod (14) to the correlated position transducer (15) which triggers the control after surpassing an upper or lower limit value of the piston position. 